How much are the racquet endorsements worth?

I know this must vary widely depending on the rank of the player (Roger and Nadal surely get paid the most. But how much?) I've never had a good grasp on how much the racquet endorsements are worth. All I know is that Davydenko and Prince fought long and hard about it when he spent all that time at #4 in the world. They paid him much less than other players ranked lower....

Well for sure free rackets for the entire time they are unders sponsorship. But even at that at one time I heard of one player only having like 8 rackets because that was all his sponsorship allowed. Something weird like that. But I would imagine millions for the top guys. Federer signed a lifetime deal with Wilson that pays him $2 million a year and all the free rackets he needs. Both Nadal and Roddick have 10 year deals with Babolat that give them millions as well. It depends on the player and where they are ranked and their appeal internationally as to the deals they get. Davydenko just isn't that appealing of a marketing presence.